Single-Transistor Variable Gain Circuit for Bidirectional RF Switching
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Solution Overview
Problem
Conventional variable gain circuits are large in size and unable to perform bidirectional amplification or switch between signal flow and cutoff, requiring multiple components and lacking flexibility in operation.
Innovation Solution
A compact variable gain circuit design utilizing a single transistor with independent bias terminals and a switch to control signal flow and amplification direction, enabling on/off operations and bidirectional amplification by adjusting bias voltages and connecting the transistor's control terminal to either a reference voltage or impedance element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional variable gain circuits use multiple components including amplifier and two SPDT switches, then the circuit can achieve variable gain functionality, but the circuit size becomes large
Solution Approach 1:
The patent combines multiple functions (switching and amplification) into a single transistor device. The transistor operates as a switch when the control terminal is connected to the reference voltage terminal, and as an amplifier when connected to the impedance element, eliminating the need for separate amplifier and switch components
Solution Approach 2:
The single transistor is designed to perform multiple functions: it can operate as a high-frequency switch, as an amplifier with variable gain, and as a signal router. By changing the connection state of the first switch and adjusting bias voltages, the same transistor component achieves different operational modes
2Adaptability or versatility
If conventional variable gain circuits use fixed amplifier configuration, then the amplification factor is predetermined, but the circuit cannot perform bidirectional amplification or switching operations
Solution Approach 1:
The circuit configuration is made dynamic through the first switch that can change the connection state of the control terminal. This allows the transistor to dynamically switch between different operational modes (switching mode and amplification mode) and enables bidirectional amplification by adjusting which terminal the control terminal connects to
Solution Approach 2:
The patent uses independent bias terminals with variable voltages to control the transistor's operating point and gain characteristics. By changing bias voltage parameters, the same hardware configuration can achieve different amplification factors and operational states without physical reconfiguration
Data Source
AI summary
A variable gain circuit includes: input/output terminals P1 and P2 configured to input/output a high frequency signal; a transistor having a signal terminal “a” connected to the input/output terminal P1, a signal terminal “b” connected to the input/output terminal P2, and a control terminal; bias terminals B1, B2 and B3, and a reference voltage terminal respectively set to a first variable voltage, a second variable voltage, a third variable voltage, and a fixed voltage that are independent of one another; an impedance element connected between the bias terminal B1 and the signal terminal a; an impedance element connected between the bias terminal B2 and the signal terminal b; an impedance element connected between the bias terminal B3 and the control terminal; and a first switch configured to switch between connecting and not connecting the reference voltage terminal and the control terminal.